Electric sensors are well known in the measurement and instrumentation industry. They are used widely in laboratories and in the field to measure physical and chemical properties of samples. A typical electric sensor is an electrochemical sensor such as pH, ion-selective, dissolved oxygen or conductivity electrode or a temperature sensor. They are available commercially in several different form factors.
A meter may have both an electrochemical sensor and an electronic temperature sensor fitted to it. This is because the parameters being measured by the electrochemical sensor may be altered by the temperature of a solution under test and so both parameters need to be measured for an accurate electrochemical sensor reading. Such temperature sensors may be resistive such as a thermistor, RTD (resistance temperature detector) or PRT (platinum resistance thermometer) or actively producing current with respect to a temperature differential across them such as a thermocouple.
Typically, voltages in the order of millivolts are output from these sensors and these voltages are interpreted by a meter to provide units relative to the physical or chemical process being measured. Two examples of meters are bench mounted meters and handheld meters. Bench mounted meters are designed to be left in a fixed place and connected by cables to the relevant sensor. Handheld meters often have an electric sensor permanently attached to them via a connector, or a cable and connector assembly.
Typically, these meters will have a display or output of some type. These displays or outputs may be a digital number or other digital indicator such as a light emitting diode (LED) display, an analogue display using a moving coil d'Arsonval meter or some type of audible output.
The meter makes a unit conversion from voltage to the relevant unit, such as pH or temperature. To enable this, the meters are calibrated by placing the probe or sensor into a solution with known chemical properties.
These types of meter may have provision for a digital output of the values being read to a computing device through an interface such as a wired RS-232 or USB (Universal Serial Bus) connection or wirelessly using Bluetooth (registered trade mark) or IrDA (Infrared Data Association—a wireless infrared communications protocol).
Handheld meters less often have a digital output suitable for reception by a computing device than a bench mounted meter due to the context in which they are intended to be used. A digital output designed for reception by an external computing device creates the possibility of logging the output of the sensor with respect to time. However, this requires the computing device to be connected to the meter at all times which may be inconvenient if the sensor and meter is located in an environment that is hostile to such computing devices.
The presence of cables, even in a fixed location benchtop meter such as may be found in a laboratory, can be a significant inconvenience or indeed safety hazard when dealing with chemicals. They may even preclude the measurement of chemical attributes in some situations. For example, this may be due to the requirement to route the cables from the vessel that a chemical is contained in, to the meter that is situated outside the container. Alternatively, this may be due to the requirement to situate the meter far from the sensor, as might be the case when measuring water in a river from a bridge so that the integrity of the sensor output may be impaired.
Each meter has a physical and electronic termination for the sensor output. For this reason, most meters only have the capability to connect to a single sensor at a time, meaning that many meters are required to measure multiple attributes of even a single experiment. These multiple meters might then have to have logging performed simultaneously, either manually, by one or more operators, or digitally, by one or more computing devices.
As mentioned above, wireless meters that attach to electrochemical sensors are known that in some way use the Bluetooth (registered trade mark) wireless communications protocol that seek to eliminate some of these problems.
One arrangement is described in US patent application with publication US2008/0041721 (granted as U.S. Pat. No. 7,719,427). This document describes a wireless pH measurement system having a portable module including a signal detecting and processing portion comprising a sensor unit for detecting a pH signal, amplifying, filtering noise, analog/digital conversion and numerical processing to generate a pH measurement signal. The system also includes a wireless transmission portion that transmits the pH measurement by a Bluetooth (registered trade mark) module. The system also includes a receiver end that comprises a Bluetooth (registered trade mark) receiver for receiving the pH measurement signal and amongst other things, displaying the pH measurement, and the receiver end also processes this signal and transmits a warning when an abnormal pH measurement signal is received.
The pHit (trade mark) of Senova Systems, Inc., Sunnyvale, Calif., United States is a handheld pH meter with a non-calibrating solid state sensor and a Bluetooth (registered trade mark) dongle. The signal from the sensor is processed by electronics in the handheld meter and can then be transmitted to a local display or to a PC, tablet computer, or process controller via the Bluetooth (registered trade mark) dongle.
The Myron L (registered trade mark) PTBT1 (pH) and PTBT2 (conductivity) of the Myron L Company, Carlsbad, Calif., United States are “pen-type” meters with a Bluetooth Smart (registered trade mark) transceiver that transmits measurements to any paired mobile device where the readings are displayed. The mobile device acts as the display for the meter effectively replacing the meter that is normally integral with a “pen-type” meter.
There are also electric sensor products that communicate with wireless protocols other than Bluetooth. An example of such an arrangement is the Seneye system of Seneye Ltd, Norwich, Norfolk, United Kingdom, which is a pond and aquarium water quality monitor. It uses a colorimetric sensor chip for pH, temperature and ammonia measurement. It requires hard wiring or external transmission box for WiFi communication of the measured data.
Another example is the Game ePool smart system. This is a wireless water chemistry monitoring system for pH, chlorine and temperature monitoring. It uses WiFi to transmit measured data to a computer for the computer to analyse the measure data. It suffers from short battery life and range.
The Go Wireless pH (registered trade mark) of Vernier, Beaverton, Oreg., United States is a general-purpose, wireless pH sensor that can be used to remotely monitor pH. It communicates pH measurements wirelessly using Bluetooth Smart (registered trade mark) from the sensor to an Apple iPad (registered trade mark) tablet computer.